The long-term objective of the principal investigator is the elucidation of the genetic epidemiology of opportunistic pathogens. The epidemiological data necessary to assess the means of transmission, virulence, and reservoirs of a pathogen provide a strong foundation for managing disease, but this data is often not available for 'minor' pathogens. Moraxella catarrhalis, an oropharyngeal commensal with pathogenic potential, will serve as a model system for genetic epidemiological analysis. Multi-locus DNA typing provides a means of assessing the genetic diversity and genetic identity in a population of bacteria. Correlation of genotype with other epidemiological factors provides a means of inferring associations between specific genotypes and transmissibility, disease state of the host, and virulence. The specific aims of this project include I) the analysis of genetic diversity in a nine year collection of M. catarrhalis isolates recovered from a Veterans Administration medical center. A random sample of M. catarrhalis isolates from each year will be genotyped using restriction fragment length polymorphisms detected by pulsed field gel electrophoresis and Southern blot analysis. Genotypic data will be entered into a data matrix, and will be used to construct a dendrogram of genetic relatedness among strains. 2) An outbreak may be due to a common source of a pathogen; this can be inferred by a concurrent increased incidence one strain. The PI will test the hypothesis that a three year peak in isolates at the Mountain Home VAMC was due to increased nosocomial transmission. This will be inferred by a decrease in genetic diversity due to the emergence of one or a few strains. In order to detect less common strains a more extensive sampling of strains recovered during the peak will be performed. 3) Genetic data will be tested for correlation with factors of epidemiological significance. Chart reviews of patient records will provide data on patient residence at the time of isolation, date of admission for in- patients, date of culture, and patient risk factors. The data will be analyzed for correlation between genetically related strains and location within the hospital, physical and temporal proximity of the patients, and specific patient risk factors. Statistically significant correlation will be used to infer the roles of transmission, environmental reservoirs, and the interaction of patient risk factors with specific strains in successful infection/colonization.